Furnaces are incorporated into forced-air systems that can supply a mix of outdoor air and "return" air. These systems can also use condensing units and evaporator coils to provide cooling. Efficiencies are measured by the Annual Fuel Utilization Efficiency (AFUE), with baseline furnace efficiencies of oil and gas (natural and propane) units typically around 80%. With high efficiency systems, this rises to 87% (oil) and 98% (gas). Energy efficiency measures in furnace systems include variable speed control of ventilation fans (tied to temperature, pressure, or carbon dioxide sensor output) and NEMA Premium^TM fan motors

Boilers can be integrated into a range of systems, from radiant slab to hot water baseboard to ventilation fans blowing across hot water coils. Like furnaces, Annual Fuel Utilization Efficiencies (AFUEs) range from 80% to 87% for oil systems and from 80% to 98% for gas (natural and propane) systems. To attain efficiencies greater than 90%, you must use condensing gas boilers. Additional efficiency options include "low mass" (low water content) boilers, increased boiler insulation, control options to reset boiler water temperature based upon outdoor air temperatures, and variable speed control of the circulating pump operation and/or the ventilation fan operation. In all cases, NEMA Premium^TM motors improve overall system efficiencies.

Direct expansion evaporator coils are incorporated into forced-air systems that can supply a mix of outdoor air and "return" air. These systems typically use furnaces to provide heating. Efficiency is measured in Energy Efficiency Ratio (EER) or Seasonal Energy Efficiency Ratio (SEER). Baseline systems often have a SEER of 10. High-efficiency units, available with SEERs of 16 and above, typically include higher efficiency compressors (i.e. scroll compressors) and condensing and evaporating fans, and increase the surface area of the condensing unit. Variable speed compressors and fans, as well as NEMA Premium^TM motors, also increase efficiencies.

Rooftop cooling and heating unit efficiencies are based on direct expansion air conditioning and furnace efficiencies. For added efficiency, install enthalpy-based economizers, heat recovery units-such as enthalpy wheels or air-to-air heat exchangers. Occupancy control, dual-speed compressors, and NEMA Premium^TM ventilation fan motors will also increase efficiency. As another option, "demand-controlled ventilation" uses a carbon dioxide sensor to determine the occupancy of the conditioned space so that outlet dampers, inlet vanes, or variable speed drives can be used to reduce the amount of ventilation air provided to the space.

Heating and cooling efficiencies are based upon either boiler or furnace and chilled water or direct expansion equipment efficiencies. Other efficiency measures include NEMA Premium^TM motors and variable frequency drives for fans, demand-controlled ventilation using carbon dioxide sensors, dual-enthalpy economizers, deck temperature reset controls, heat recovery units-such as enthalpy wheels or air-to-air heat exchangers and optimum start-stop strategies.